From the related art, an inkjet printer is known (for example, JP-A-2008-213162) which includes a detachable main tank, a sub tank that stores ink supplied from the installed main tank, and an image recording unit that discharges the ink stored in the sub tank and prints an image. In the inkjet printer having the above configuration, internal spaces of the main tank and the sub tank are opened to the air. For this reason, when the main tank is installed in the inkjet printer, the ink moves due to a water head pressure so that the liquid level of the main tank and the liquid level of the sub tank are aligned with the same height by the difference between a water head in the internal space of the main tank and a water head in the internal space of the sub tank (hereinafter, referred to as “water head difference”). Then, when the residual amount of the ink detected by a residual amount detection sensor is less than a threshold, the inkjet printer displays the fact that the ink is empty, or prohibits the discharge of ink through the recording unit.
In the inkjet printer, when the ink is stored in the sub tank as much as air does not enter an ink flow path extending from the sub tank to the image recording unit, the ink discharge of the image recording unit is prohibited. Thus, a so-called air-in, in which the air enters the flow path, can be prevented in the inkjet printer.
When the main tank is exchanged, ink flows out from the main tank to the sub tank. If a residual amount detection sensor for detecting the ink is provided in the sub tank, the ink flows from the main tank to the sub tank, and eventually, the detection signal of the residual amount detection sensor changes. When the detection signal of the residual amount detection sensor changes, it is possible to erase the indication of the empty on the display and to cancel the prohibition of the discharge of the ink. However, when the ink flows out from the main tank to the sub tank and the time is required until the signal output from the residual amount detection sensor changes, the empty indication on the display does not disappear during that time, whereby a user may be kept waiting until the image recording is performed.